This invention relates to a ski boot toe binding of the type in which a metallic main body having a toe holder at one end thereof is rotatably mounted on a base plate and yieldably supported and held in position thereon by a horizontally disposed compression spring. This spring is provided in a cavity in the main body and urges a piston against a cam member integral with or secured to the base plate.
The ski boot toe binding of this general type is known as shown, for example in U.S. Pat. Nos. 3,027,173 and 3,430,971.
In the toe binding according to U.S. Pat. No. 3,027,173, a pivot pin projects through an elongated vertical opening in a main body and rotatably supports the main body on the base plate. The pivot pin has a flat face on the front side thereof against which the flat end of a piston is urged. Thus, the pivot pin itself also functions as the cam member. In such a known toe binding, when a lateral force is applied to a ski boot toe fitted to this binding, the main body first receives a rotational force tending to rotate it about the pivot pin and presses against the surface of the pin at the end thereof. Accordingly, at the time of rotation of the main body, a relatively high sliding frictional resistance is developed between the main body and the surface of the pivot pin at the end thereof. Thus, the main body has to rotate against the frictional resistance and the force of the piston will be urged against the flat face by the spring. Also, frictional resistance is developed between the main body and the surface of the pivot pin at the end thereof when the main body is displaced to a lateral position short of a toe releasing position and then returns to the normal toe holding position. Therefore, the restitution force of the spring is reduced by the frictional resistance.
The restitution force of the toe binding is such a force as to return or restore the binding from the displaced position short of the toe releasing position to the normal toe holding position. It is said that toe bindings having higher restitution forces are more reliable and safe, since the return of the binding from the displaced position to the normal position is rapid.
In order to provide a higher restitution force to the binding, a spring having higher compression force may be used, but the binding force caused by this spring force results in the frictional resistance also becoming greater. In a toe binding which has to release the boot toe at a predetermined value of the lateral force, it is impossible in practice to increase the spring force in order to obtain a higher restitution force.
In the other known toe binding shown in U.S. Pat. No. 3,430,971, a main body is rotatably mounted on a pivot pin, which in turn is fitted on a base plate and projects through an elongated slot in a piston. The piston is urged by a spring against a cam plate secured on the base plate. In such a toe binding, when the main body receives a lateral force causing it to rotate about the pin, the piston, which rotates together with the main body, is pressed against the pivot pin, thereby producing a sliding frictional resistance therebetween. Thus, the movement of the piston is somewhat interfered with by the frictional resistance with the result that the restitution force of this binding is also reduced as in the case of the known binding shown in U.S. Pat. No. 3,027,173.
Furthermore, in these known toe bindings set forth above or other toe bindings, a ski boot toe holder, which is provided at one end of the main body, is made of metal and formed to receive both front side edges of the boot toe. Accordingly, when the boot toe is displaced toward the toe releasing position by a lateral force applied thereto, a relatively high sliding frictional resistance is developed between the contact surfaces of the front side edge of the boot toe and the metallic toe holder. Such a frictional resistance is also developed when the main body is displaced to a certain position short of reaching the toe releasing position and then returns to the normal position thereof. The reduction of the restitution force of the binding caused by such frictional resistance is something which should not be neglected in a safety binding.
In order to reduce such frictional resistance, it has been proposed to attach thin synthetic resin plates having low coefficient of friction to both inner sides of the metallic toe holder, against which both front side edges of the boot toe will bear. In such case it is necessary to form concave areas at both inner sides of the metallic toe holder to snugly receive the synthetic resin plates therein. However, the synthetic resin plates do not adhere to the metal surface permanently and it has been experienced that they tend to become disengaged and to fall off.
Another proposal which has been made to reduce the frictional resistance between the toe holder and the boot toe is to form the toe holder entirely of synthetic resin having low coefficient of friction. However, when such a toe holder is used together with a heel binding which urges the boot forwardly by a spring force, the toe holder made of synthetic resin is partially deformed by the strong forward pressure of the heel binding due to the elasticity of the resin. Although such deformation of the toe holder is relatively small in the normal toe holding position, it becomes larger as the toe holder is displaced toward the toe releasing position and, therefore, the accuracy of the binding force is somewhat affected. In addition to the above disadvantages, the toe holder made of synthetic resin is relatively fragile when external forces are applied especially at low temperatures.